Limited torque drive for electrically operated rotary tooth brush



Nov. 25, 1958 P. HUSSAR 2,861,462

J. LIMITED TORQUE DRIV OR ELEC CALLY OPERATED ROTAR TH BRU Filed Oct. 1956 INVENTOR. MW @4444 United States Patent LIMITED TORQUE DRIVE FOR ELECTRICALLY OPERATED ROTARY TOOTH BRUSH Joseph P. Hussar, Weymouth, Mass., assignor to Leslie N. Baker, Scituate, Mass.

Application October 15, 1956, Serial No. 615,868

6 Claims. (Cl. 74423) The present invention relates to an improved structure in an electrical toothbrush, and particularly to a further improvement and modification of my previously filed application Serial No. 583,454 filed May 8, 1956, and still further to an improved structure over co-pending applications Serial No. 441,396 for an application in a rotary toothbrush to Leslie N. Baker and Serial No. 272,810 for a rotary toothbrush to Leslie N. Baker filed February 21, 1952, now Patent No. 2,766,470.

The problems presented in the design of an electrically operated toothbrush are substantially set forth in my copending application. The desirable design characteristics of such a toothbrush as at least partly set forth in the above-mentioned application include the provision of a brush head and handle of compact size suitably shaped to conform with operating requirements; a brush having sufiiciently long bristles to reach the recesses between teeth; a structure which is sufficiently rugged to withstand substantial stresses on the driven shaft which rotates the rotating brush; a bearing structure and arrangement which supports the shaft and which can satisfactorily withstand leverage action on the driven shaft; and suitable means for slowing or stopping the rotation of the brush when excess pressures are applied to it. In addition to these desirable design characteristics, it is particularly desirable to provide a structure which is compact in nature and which may readily have portions of its structure pre-assembled. In particular, it is desirable to provide a structure in which the clutch and drive means are sub-assembled and are then subsequently assembled with the main portion of the housing in a final assembly procedure.

The present invention provides a structure which satisfactorily attains the objects and design features enumerated above and inparticular provides a structure in which the head of the toothbrush has substantially less depth or thickness than structures heretofore designed. Further, the present invention provides a structure in which there is less friction and clutch slippage in the moving element. Principally the present invention makes possible a manufacturing technique in which the clutch and drive members are first sub-assembled and then completely assembled in the housing. Further features of the present design provide means by which the clutch tension is a less critical factor in the manufacture of the unit. These and other objects of the present invention will be more clearly understood when considered in connection with the accompanying drawings, in which: Figure 1 illustrates a particular cross sectional elevation of the electric toothbrush member with the cut-away portions taken substantially along a longitudinal symmetrical line.

- Referring to the drawings, there is illustrated an electrically operated brush having an inclosing casing 1 which is preferably formed in two sections 2 and 3 which fit together along a tongue and groove joint 4. The casing may be made of any suitable material'but preferably is made of a plastic such as polystyrene acetate or nylon. At one end of the casing, there is provided an enlarged section 5 adapted to contain a motor drive which is not shown but which may be of any conventional means suitable for driving the drive shaft 6 at desired and selected speeds. The drive shaft 6 is longitudinally located in the casing 1 and extends through an axial opening 7 in this casing. Suitable bearing means are provided along the casing for coaxial support of the driving shaft 6. Such bearing supports may consist of ball-bearing elements or if desired other means, as for example, neck portions 8 formed in the casing 1 and adapted to bear against the driving shaft 6. At the other end 9 of the casing 1, there is provided an enlarged opening 10 adapted to receive the driven elements of the invention. This opening it) may be substantially cubic in shape with an opening formed in the section 2 of the casing 1 at 11. This opening is preferably symmetrically arranged with respect to the enlarged opening 10. The driving shaft 6 which projectsinto the enlarged opening or cavity 10 engages the nylon bevel gear 12. This gear 12 has an enlarged depending gear hub 13 which projects downwardly below the level of the driving shaft 6. A steel press fit shell 14 is positioned over this hub 13 and forms a lower bearing member for the nylon gear 12. This gear 12 is also provided with a coaxial opening which is covered at one end by the steel shell 14. This coaxial opening is wider at its lower end than at its upper end and tapers along a mid-section area towards this narrower upper end. A driven shaft 15 is partially positioned within this opening in the gear 12. The shaft 15 has a lower end with an outershape substantially conforming to the wall contours of the opening in 'the gear 12. The shaft 15 is movable in a direction longitudinal to its length over a distance limited by the constricted opening in the gear at one end and the steel shell 14 at the other end. This shaft 15 is also provided with a coaxial recess 17 extending upwardly from its base. This recess which may be tapered as illustrated has positioned within it a helical spring 18 and ball-bearing 19 which are engaged one with the other with the ball-bearing positioned above the spring and in contact with the upper wall of the recess 17. The lower end of the spring 18 fits over a .boss 20 formed at the center of the shell 14. This boss 20 acts as a bearing end for the spring 18. A recess is provided in the lower portion of the shell 14 with, the

recess adapted to fit over the locating stud 21'with the stud 21 projecting upwardly from the lower surface of the cavity 10. If desired, the stud 21 may be formed vof a hardened materialto-avoid; wear and damage due to the rapid rotation of the gear 12. :This stud 21j acts as alocatirig means'for-thegear assembly. i l

The upper end of the shaft 15 projects through the opening 11 and is coaxially mounted in this opening 11 by means of a nylon bushing 22. The bushing 22 is provided with a recess section 23 in which there is located an O ring 24. The O ring 24 is secured in position and is formed as an integral structure with the bushing by means of the steel shell member 25 which is formed of an angular'inwardly extending flange and an upwardly extending apron surrounding the lower portion and sides of the nylon bushing 22.

The gear 12 is suitably spaced from the bushing and steel shell 22 and 25, respectively, by an annular boss 27 formed in the upper portion of the gear 12. This gear 12 is also longitudinally located from contact with the lower wall of the cavity 10 by suitable selection of the length of the stud 21.

A threaded section 29 is provided at the upper end of the driven shaft 15 for suitable attachment of the brush.

The brush may be of the type generally illustrated in Ce Patented Nov. 25, 1958 mv-co-pending application Serial No. 583,454, with the exception that the collar-engaging portionofthe brushshould be provided with an internally threaded recess adapted to receive the threads 29.

\ Suitable-modifications'of'the brush may. bemadein ing 22, shell 2'5 andO ring 24 may be assembled as a unit-and also inserted into the casing-1 without any substantial'difiiculty being presented in manufacturing techniques. It may be noted'that the nylon bushing may be secured inthe casing by suitable means; as for example, by threading a short portion of the shell 25 and section 2 about the opening 11, with these two threaded sections interengaging one another when the bushing is located in the casing.

It should be understood that the outer walls of the driven shaft 15 in the area within the opening in the hub13- ofthe bevelled gear 12 are friction engaging and are adapted to coact with the walls of the opening to drive the driven shaft 15. Accordingly the inner walls of the opening within the gear 12 and thecorresponding walls of 'thedriven shaft 15 should be roughened or otherwise suitably treated to form friction engaging coacting surfaces. It may alsobe-noted that the bevelled gear 12 and the he-velledgearformed on the shaft 6 may be of the conventional type with each gear being provided with interengaging teeth.

Having now describedmy invention, I claim:

a 1 Anelectrically operated toothbrush having a drive shaft with a first bevel gear at the end thereof, a second bevel gear interengaging the first and having a hub with a coaxially formed opening formed therethrough, said opening beingtapered from one end to the other and providing an engaging friction surface, a driven shaft positioned partially within said opening and coaxially aligned therewith, and having an outer surface adapted to. frictiorlally engage said opening, a recess formed in the portion of the driven shaft within said opening, spring means positioned within said recess urging said driven shaft and gear in friction contact, and means retaining the drive shaft and gear in operative association.

' 2. In an electrically operated toothbrush having a driveshaft with a first bevel gear at the end thereof, a second: bevel gear interengaging the first bevel gear and having an axially aligned hub, an axial opening extending through the second bevel gear and hub, means forming a frictionallyengagablesurface-on thewall of said opening, a driven shaft positioned at least partially within and coaxially aligned with said-opening with a friction engaging surface adapted to be engaged with said firstmentioned surface, means permitting limited longitudinal motion of said driven shaft in and out of frictional engagement with said first-mentioned surface, a retaining shell capping said hub and covering the end of said opening, and means disposed Within the opening and bearing in part against said shell for normally tensioning said surfaces together,

3. A device as set forthin claim 2 wherein said driven shaft has formedtherein a coaxial bore extending partially inward from the end adjacent'said shell with said means for tensioning said surfaces together comprising a spring means having one end bearing against said shell and the other against said driven shaft within said bore.

4: A device as set forth in claim 3 wherein said opening has a larger diameter at one end than the other with anint'er-media'te"tapered section, said tapered section having formed thereon said first-mentioned friction engaging surface.

5. A device as set forth in claim 2 wherein the end of the opening at the hub is of a larger diameter than the other end, and with an intermediate tapered section between said ends, said tapered section having formed thereon said first-mentioned friction engaging surface.

6. In an electrically operated toothbrush including a casing-having a cavity formed therein, a drive shaft with a first bevel gear projecting into said cavity, a second bevel gear having a hub and means forming an axial opening through said gear and; hub, means mounting saidsecond gear Within said cavity in operative engage ment with said first gear, a driven shaft partially positioned within said opening and extending outwardly of said casing, means forming complementary friction engagable surfaces; on said driven shaft and said opening, means permittinglimited longitudinal movement of said driven shaft into and out of frictional engagement, a shell capping said'hnb with a depression formed in said shell in coaxial alignment with said driven shaft, boss means extending from said casing within the cavity and engaging said depression as a locating stud, and means bearing in part against said shell opposite said depression and tensioning said complementary surfaces toward one another;

References Cited in the file of this patent UNITED STATES PATENTS 2,010,210 Whitt Aug. 6, 1935 2,766,470 Baker Oct. 16, 1956 FOREIGN PATENTS 919,905 Germany Nov. 8, 1954 

